Meandering Process Research Articles

Gleysols genesis and fluvial dynamics in a quaternary floodplain of the meandering river, Minas Gerais, Brazil

Soils are good indicators of the stability of environmental systems. In meandering river floodplains, they assess river channel morphology, incision process, groundwater level dynamics, and avulsion processes. The morphological properties and physicochemical attributes give gleysols unique characteristics about formation conditions and evolution degrees related to fluvial dynamics, thus allowing elaborate models of floodplain evolution in meandering rivers. This manuscript aimed to analyze the relationship between gleysols evolution and fluvial dynamics, in the quaternary floodplain of a meandering river, in the Mogi Guaçu River basin in the State of Minas Gerais. We described three profiles, in concave and convex margins of the river, identifying facies and considering the morphological characteristics of the gley horizons. Physicochemical analyses, determination of major and minor elements, and oxides were carried out on the samples of horizons and deposits of the profiles. For the characterization of the river channel, morphometric parameters were measured. Concentrations of silica, titanium dioxide, alumina, ferric and manganese oxides, plus the molar relations of provenance (P), leaching (L), parent material (M1 and M2), oxidation (O), hydrolysis (H), and the alteration geochemical index (CIA-K) were determined to compare the profiles pedological evolution. The three analyzed profiles were classified as typic Dystrophic Tb Haplic Gleysol (P1 and P2) and typic Alic Tb Haplic Gleysol (P3) so that the relation silt/clay demonstrated profile 3 to be the most evolved (weathered). Concentrations and behavior of oxides, associated with molar relations and conditions of the surfaces S II and S III of the flat floodplains morphological, demonstrated that the meandering process, with avulsion linked to erosion and deposition, affects gleysols evolution, suggesting genesis with compound or polygenetic profiles. Under a cyclical interpretation, the evolution of gleysol profiles, with truncation and horizon overlaying, reflects processes of avulsion, incision, and floods, as well as are proxies for interpreting the quaternary evolution of the Mogi Guaçu River meandering process.

Channel Processes Disconnectivity in Rivers Hydromorphology

The present paper deals with five main structural levels of channel processes and channel patterns due to disconnectivity of fluvial processes. River braiding is related to existence of point, bar, channel (island), anabranching and large distributary channels (located in the deltas of large and largest rivers). Meandering is related to sinuosity of the flow and formation of complex loop and large meanders, the dimensions of which are larger than those corresponding to the water content of the river, and the meanders of the meandering belts. Due to the instability of the straight flow, the structural levels of the straight single channel are distinguished by their size: pool hollows on the riffles, reaches between adjacent bends and segments of braided channel, sections between single branches and stretched stretch areas along the bedrock banks or in the incised channel. Each structural level is related to the previous one forming scaling sequence (middle and side channels are the basis for the formation of branches and bends, etc.), representing genetic series, although in some cases they may have a different origin (intra-floodplain intercepts, relics of delta branches, etc.). The meandering process happens over various scales in both braided and straight channels. The formation of structural levels is governed by river size, geology, effective discharges and local drivers.

ANTHROPOGENIC INFLUENCE UPON THE SUKIL RIVER BED FUNCTIONING

A river bed is a main indicator of the changes, including manmade ones that take place in their catchment basins. These changes are reflected in the river beds functioning, especially within the catchment basins located in the Ukrainian Carpathians. These basins have been noticeably affected by human impact during last century. The Sukil River (left tributary of the Svicha River) is one of them. By the relief morphology features and geologic-geomorphologic structure the Sukil River basin is divided into three parts: mountain, premountain and plain. The river bed within these three parts is characterized by noticeable difference in morphological and morphodynamical parameters. And the reaction of the riverbed on the manmade changes also is different in all three parts. First of all, it is a deforestation, agriculture, unauthorized gravel intake within the river bed and floodplain, river bed straightening, river bank consolidation and flood protection dikes constructing, melioration and ponds constructing etc. Research results ascertained noticeable difference between manmade influences in different parts of the catchment basin, especially the effects on the river beds and their functioning. In the mountain part the moderate impact dominates and is mainly presented by timber falling which has caused significant sediments runoff increasing during the floods of 2008 and 2010. In the premountain part the strongest impact is done by the unauthorized alluvium mining in the river bed. It caused increasing in the river bed morphodynamics and reinforcing of the linear and local side erosion. The erosion processes threat the roads and buildings within the river valley. The plain part of the river basin is most transformed. The river bed strengthening is carried out since the middle of ХХ-th century which was accompanied by the dikes and drainage network constructing. As the result many boggy areas were drained, the morphology of the Sukil river bed was changed, the meander process was stopped. But the tendencies to renaturalization of the river valley are observed during the last years. Conducted research are important for the rivers renaturalization and providing the strategy of sustainable development in Ukraine in the matter of natural resources protection and management. Key words: channel morphodynamics; Sukil River; anthropogenic influence; mountain, premountain and plain parts of the basin.

De meanderende Oude Rijn

The meandering Old Rhine. A reconstruction of the course of the river in the Roman period and the early Middle Ages Using the knowledge of river processes that control river dimensions and meandering, a reconstruction is made of the river pattern of the Old Rhine between Leiderdorp and Katwijk in the Netherlands. The river pattern changed from a straight river in the Roman period to a meandering river in the early Middle Ages and this pattern was fossilized by the damming of the river at the start of the late Middle Ages. Using archaeological results from the area, the meandering processes are modelled and the archaeological expectations of different areas are assessed. The assessment shows that normally used reconstructions of the development of the Old Rhine delta are inconsistent and that in large areas of the former delta no archaeological finds can be found from prehistoric or Roman times because they were eroded by a meandering river.

Doing comparative urbanism: comparative conversation as tactic

ABSTRACT This paper offers comparative conversation – that is, formal comparison across cases invoked in sequential, recursive, and incremental fashion – as an experimental tactic for thinking the urban across difference. It provides a chronological, self-reflexive account documenting the emergence, operationalization, and achievements of comparative conversation across collaborative urban experiments in Shenzhen and London. The account showcases the emergence of comparative conversation as a function of the intersection between the personal geographies and comparative ambitions of the researcher and how the meandering and complex process of the comparison led to analytical and conceptual innovation. In so doing it contributes to ongoing calls for the renewal of the comparative method by positively demonstrating the role of the researcher in making viable an experimental comparison by leveraging the shared features of different urban contexts as a generative starting point for comparison. The paper concludes by suggesting that all comparative tactics must generate concepts of value and discusses the mediation between risk and rigor in novel forms of comparison.

Exploring intergroup conflict and community-based participatory research partnerships over time

Community-based participatory research (CBPR) is a growing practice by which academics and community partners conduct collaborative health-based research. While CBPR fosters productive partnerships, there is increasing research on interpersonal group dynamics and the ways that intersecting factors, such as gender and ethnicity, affect the social interactions within CBPR. This paper explores the tensions inherent in large interdisciplinary community-based participatory research partnerships, through the examination of a long-standing community–academic partnership focused on advancing public health. Nine qualitative interviews were conducted between November 2019 and January 2020 with steering committee members from a long-standing collaborative partnership that conducts research to inform public health action. While the collaborative process was generally positive, we also uncovered less pleasant aspects of CBPR projects that are infrequently discussed in the literature, such as role confusion and power dynamics. Leadership style was seen as the driving force shaping how other team concerns were perceived. Not having structures in place to facilitate relationship development, or clear documentation of procedures, rules and norms, led to team complications. Team members suggested that a renewed focus on organisational structure would contribute to role clarity and organisation. The results highlight the complexity of working on interdisciplinary mixed community–academic teams, specifically the ways in which interdisciplinary, collaborative research can be a complicated, meandering process, often without clear-cut answers to sometimes simple questions.

Autogenic translation and counter point bar deposition in meandering rivers

AbstractAlthough it has long been recognized that deposition along meandering rivers is not restricted to convex banks (i.e., point bars), the consensus is that sediment deposition on concave banks of channel bends mostly occurs when meander bends translate downstream because erosion-resistant barriers inhibit their lateral migration. Using a kinematic model of channel meandering and time lapse satellite imagery from the Mamoré River in Bolivia, we show that downstream translation and associated concave bank deposition are essential, autogenic parts of the meandering process, and resulting counter point bars are expected to be present whenever perturbations such as bend cutoffs and channel reoccupations create short bends with high curvatures. The implication is that zones of concave bank deposition with lower topography, finer-grained sediment, slack water, and riparian vegetation that differs from point bars are more common than previously considered.

MORPHODYNAMIC CLASSIFICATION OF CHANNEL OF SUKIL RIVER

The morphodynamic classification of the Sukil river channel made it possible to determine the hydromorphological processes and to study the factors that determine them. The channel was classified according to the method of R.S. Chalov. Three main classification criteria were taken into account: the geomorphological type of conditions for the formation of the channel; the type of channel processes; the mophrodynamic type of channel. According to the geomorphological type of channel-forming conditions, the channel is divided into the incised channel – located mainly in mountainous and semi-mountainous parts with a characteristic the narrow valley, laid in sandstones, siltstones, and argillites; confined channel – located in intermountain basins, with one bank of channel composed of bedrock, and the other – of Quaternary sediments; wide-floodplain channel – mainly located in the lower part of the channel on the Stryi-Zhydachiv basin, laid in the Quaternary deposits of loams and sands. According to the type of channel processes, the channels with developed alluvial forms and without developed alluvial forms are dominant. Together they make up 2/3 of the channel. Other types of channels are wide-floodplain – characterized by slow flow and stable development of the meandering process, and rapid-waterfall – located in the upper reaches of the channel. The latter is characterized by a stormy current and the presence of numerous rapids made of boulders and wood. There are 3 main morphodynamic types of the channel – meandering, branched, and straightforward, and 6 their subtypes. Meandering, incised channels are characterized by structural meanders, their shores are composed of hard rocks, mostly sandstones. The meandering confined channels are defined by the root bank in the apical part and the upper wing along the root bank, which leads to the formation of segmental and blockage convolutions. Meandering, broad-flooded channels are characterized by longitudinal displacement of meanders, their convolutions are segmented, rarely loop-shaped. The coefficient of meandering gradually increases from the mountainous part of the channel to the plain one (1.10–1.35). Branched type is represented by a single complex and floodplain-channel subtypes. The size of the islands that divide the channel into arms is from a few meters to 350–400 m. The straightforward type of channel is widespread and is 1/3 of the total length of the river. Key words: channel type; straightforward; branched; meandering; incised; confined; floodplain.

Geomorphologic Analysis of Small River Basin within the Framework of Fractal Tree

This paper presents the modified framework of geomorphologic analysis based on the concept of fractal tree. Especially, it is intended to provide hydrologic practitioners with the information on the fractal property of small river basins. To this end, the complete drainage path network is applied to a growth process of a fractal tree for the basin of interest by connecting a channel network to overland drainage pathways. The growth process of a fractal tree would occur only within the limited region possessing channel flow properties in a natural river basin. The exponent of the intra basin type of Hack’s law could show a variable trend in small river basins mainly due to anisotropic property of the catchment planform. The bifurcation process of a drainage path network might be more sensitive to the growth step of the fractal tree than the meandering process of drainage path segment. The fractal dimension from the sinuosity of a channel segment is relatively stable compared to the one from the bifurcation process of the network, so that the geomorphologic features of a small river basin can be characterized by the anisotropic property of catchment planform as well as the bifurcation property of drainage path network with the growth of the fractal tree.

Estimation and prediction of the oscillation pattern of meandering geometry in a sub-catchment basin of Bhagirathi-Hooghly river, West Bengal, India

Meandering is the winding curve or bends in a river within the floodplain area. Though it is a natural process, it affects the populace by the resultant effect of lateral migration with bank erosion in the floodplain area. The present sub-catchment basin (Nabadwip–Kalyani stretch) of the Bhagirathi-Hooghly river is a vital lifeline of southern West Bengal, which offers adequate water for irrigation, industrialisation, and human habitation. This region is experiencing a favourable geomorphic change through river bank line changing with bank erosion and sinuous meandering. Illegal sand mining and monsoonal flood enhances the meandering process and triggers the reduction of settlement and cropland. The present study elaborates on the migration tendencies and meandering geometry of this zone and tries to predict the future river centerline position in a sinuous course. The study area is divided into 30 cross-sections, which reveals the increasing trend of lateral migration and erosion behaviour towards the eastward section of this region. The spatial and temporal shifting of river centerline and resultant migration observes and predicts through the migration coefficient approach (Hasegawa in Proceedings of the Hokkaido Branch, Japan Society of Civil Engineering, pp 197–202, 1977; Ikeda et al. in J Fluid Mech 112:363–377, 1981. https://doi.org/10.1017/S0022112081000451 ; Motta et al. in Geomorphology 163–164:10–25, 2012. https://doi.org/10.1016/j.geomorph.2011.06.036 ) by Arc GIS v 9.3.1. This model indicates the trend of channel width decreasing, with increasing near bank velocity in the crescent of meandering bend in future. The simulated and predicted centerline validates by positive linear relation (R2) and lowest RMSE value in few cross-sectional areas. The oscillation character of meander signifies the amount of discharge in the sub-catchment basin. The unpredictable behaviour of the migration shows a rapid change of meandering geometry through the increasing nature of bank erosion possibilities with peak discharge during monsoon. The study predicts future centerline of the meandering channel and the information on river migration, which will contribute to the plan on bank erosion and denote the vulnerable zonation.

Fate of pioneering vegetation patches in a dynamic meandering river

AbstractFluvial biomorphodynamics in actively meandering rivers entail interactions between hydromorphodynamics and pioneering tree species that have eco‐engineering effects. Here we study spatiotemporal patterns of vegetation patches smaller than 150 m2 in a 4 km reach of the river Allier in France in order to unravel causes for tree persistence and mortality and identify spatial trends across the river valley. To this end we analysed aerial photographs by object‐based image analysis over a period of 56 years and tracked individual patches through time. Furthermore the cover and surface age of the study reach were classified. The large‐scale shifts of channels, bars and vegetation are consistent with the meandering process and chute cutoffs. However, the spatiotemporal patterns of the vegetation patches are surprising in that they are ubiquitous and have ages up to decades on the highly dynamic meander belt, but hardly expand into larger vegetation patches. Patches disappear exponentially as a function of their age, and faster so in the last decades. Causes are amalgamation into the riparian forest flanking the meander belt and mortality likely due to desiccation or erosion. Patches have a higher probability of survival when further away from the active channel and closer to high vegetation patches and valley boundary. The window of opportunity of vegetation settlement widens towards the valley boundaries and in floodplain lows of former channels and chutes. These results imply a gradual cross‐valley gradient of riparian vegetation settling, survival and succession. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.

Ceci n’est pas un Dessin: Notes on the Production and Sharing of Fieldwork Sketches

Whereas the topic of how anthropologists link intimate written information gathered in the field with public production of knowledge in academic format – the so-called “writing culture” (an expression originated in Clifford and Marcus 1986) –, seems all but exhausted today, little attention has historically been given to the place and goals of sketching as part of that meandering process. The present contribution discusses the ontological and social conditions for the production and reception of knowledge-in-the-field sketches, on drawing as practice and as materiality, and on its bordering with writing.

Statistical analysis of a field database to study stability effects on wind turbine wake properties

Within the frame of the French project ANR SMARTEOLE, a 7-month measurement campaign had been set-up in the north of France to study the wake behaviour of 2 wind turbines, with a set-up using scanning LiDAR scenarii that captured the wakes of 2 wind turbines for different degrees of interactions. An extensive statistical study of the wakes behaviour under neutral atmospheric stability conditions has been already performed. The present study focuses on the effects of other stability conditions on the wake developments and on the meandering process.

О ПРОИСХОЖДЕНИИ ЧЕТКОВИДНОЙ ФОРМЫ РУСЕЛ МАЛЫХ РЕК КРИОЛИТОЗОНЫ, "Геоморфология"

Четковидные русла, характеризующиеся закономерным чередованием озеровидных расширений и соединяющих их узких проток, распространены в криолитозоне и считаются типичным примером деградации полигонально-жильных структур и мерзлоты в целом. Другие мнения связывают генезис расширений с закреплением русловых форм в результате их промерзания. Однако специальные исследования, направленные на изучение механизма образования четковидной структуры русел малых рек криолитозоны, до сих пор не проводились. На основе сопоставления существующих гипотез происхождения с данными об их морфологии, распространении и характере залегания мерзлых пород в статье предложена наиболее вероятная схема формирования четковидных русел. В частности выявлено, что они не являются признаком деградации мерзлоты и полигонально-жильных структур, так как последние представляют собой вторичные формы на пойме по отношению к руслу. Четковидные русла - полигенетические образования, связанные с термокарстом, избирательной термоэрозией, русловыми и ледовыми процессами, роль каждого из которых зависит от локальных природных условий. Выделен особый тип - четковидные извилистые русла, которые представляют собой реликты свободно меандрирующих и являются признаком снижения руслоформирующей деятельности рек, причинами которой могли быть как изменения стока воды, так и агградация мерзлоты в долинах. Более детальный анализ причин и установление возраста трансформации извилистого русла в четковидное позволит использовать их для реконструкции палеоклиматических и палеоги-дрологических изменений в криолитозоне.

Meandering Process and Migration Architecture: Based on the Nowitna River

The meandering process has always been the topic through years and still remains a lot of unsolved mysteries. One of the most important focus is the migration architectures and models that the meandering channels follow. This article chooses the Nowitna River as the study object of the typical meandering river with high migratory processes. Though the high-resolution historical satellite images by the techniques of Google Earth and ACME Mapper, 50 meanders in the river is studied and 6 of which are chosen for meticulous characterization. During the process, the planform structure of meandering channel is re-examined and 29 kinds of architecture elements are systematically established. More importantly, in order to make a fine quantitative characterization of the channel structure of meandering river, 5 kinds of characterization parameters are proposed, extraordinarily, the parameters of the difference of along-current deflection angle, a difference of counter-current deflection angle, and expansion coefficient, these three are firstly brought forward and applied introduction. In addition, the conception of sinuosity index and curvature are also different from the original definition. Though these architectures elements the meandering process and migration structure of the Nowitna River is demonstrated. 6 kinds of planform migration structures is revealed with the quantitative characterization of characterization parameters and 9 species of meandering channel migration patterns are concluded and discussed.

Geomorphic criteria for distinguishing and locating abandoned channels from upstream part of Mun River, Khorat Plateau, northeastern Thailand

In order to develop geomorphic criteria for distinguishing and locating abandoned channels and meandered belts, in this paper we examined geomorphologic characteristics from the Mun River, one of the main rivers in the Khorat Plateau, northeastern Thailand. Upstream of Mun River originated at southwestern rim of the Khorat Plateau where the river now cuts through sandstone basement. Meandering process shaped meander from upstream ending at low-lying plain about 30 km downstream from the Mun Bon Dam reservoir, and this process displays given values of geomorphic parameters including sinuosity index (SI), channel width (W) and radius of curvature (Rc). Sinuosity index was calculated to express the sinuosity of the channel. The relationship between W and Rc helps to predict channel stability and also comprehend the possibility of cutoff process. As a result, paleo- and recent flow directions of the Mun River are similar from southwest to northeast. Geomorphic parameters from eight river reaches have changed through time since 1974–2015. Two abandoned channel belts were identified, and they own an average channel width of 35 and 16 m, whereas the Mun River nowadays is of 12.7 m. SI values of two abandoned channel belts are categorized as meandering river system. Relationship between meander migration rate and bend curvature suggests that the Mun River possesses low erosion rate between 0.71 and 2.64 m/year since 1974 to the present. This rank of Rc/W ratio suggests stable state of river bank migration. Different migration indicates discontinuous meandering process from individual belt. Lateral migration rate was also decreased after Mun Bon Dam was constructed upstream.

A Novel Explicit-Implicit Coupled Solution Method of SWE for Long-term River Meandering Process Induced by Dambreak

Large amount of sediment deposits in the reservoir area can cause dam break, which not only leads to an immeasurable loss to the society, but also the sediments from the reservoir can be transported to generate further problems in the downstream catchment. This study aims to investigate the short-to-long term sediment transport and channel meandering process under such a situation. A coupled explicit-implicit technique based on the Euler-Lagrangian method (ELM) is used to solve the hydrodynamic equations, in which both the small and large time steps are used separately for the fluid and sediment marching. The main feature of the model is the use of the Characteristic-Based Split (CBS) method for the local time step iteration to correct the ELM traced lines. Based on the solved flow field, a standard Total Variation Diminishing (TVD) finite volume scheme is applied to solve the sediment transportation equation. The proposed model is first validated by a benchmark dambreak water flow experiment to validate the efficiency and accuracy of ELM modelling capability. Then an idealized engineering dambreak flow is used to investigate the long-term downstream channel meandering process with non-uniform sediment transport. The results showed that both the hydrodynamic and morphologic features have been well predicted by the proposed coupled model.

Determination of real-time predictors of the wind turbine wake meandering

The present work proposes an experimental methodology to characterize the unsteady properties of a wind turbine wake, called meandering, and particularly its ability to follow the large-scale motions induced by large turbulent eddies contained in the approach flow. The measurements were made in an atmospheric boundary layer wind tunnel. The wind turbine model is based on the actuator disc concept. One part of the work has been dedicated to the development of a methodology for horizontal wake tracking by mean of a transverse hot wire rake, whose dynamic response is adequate for spectral analysis. Spectral coherence analysis shows that the horizontal position of the wake correlates well with the upstream transverse velocity, especially for wavelength larger than three times the diameter of the disc but less so for smaller scales. Therefore, it is concluded that the wake is actually a rather passive tracer of the large surrounding turbulent structures. The influence of the rotor size and downstream distance on the wake meandering is studied. The fluctuations of the lateral force and the yawing torque affecting the wind turbine model are also measured and correlated with the wake meandering. Two approach flow configurations are then tested: an undisturbed incoming flow (modelled atmospheric boundary layer) and a disturbed incoming flow, with a wind turbine model located upstream. Results showed that the meandering process is amplified by the presence of the upstream wake. It is shown that the coherence between the lateral force fluctuations and the horizontal wake position is significant up to length scales larger than twice the wind turbine model diameter. This leads to the conclusion that the lateral force is a better candidate than the upstream transverse velocity to predict in real time the meandering process, for either undisturbed (wake free) or disturbed incoming atmospheric flows.

Estimation of floodplain aboveground biomass using multispectral remote sensing and nonparametric modeling

Floodplain forests serve a critical function in the global carbon cycle because floodplains constitute an important carbon sink compared with other terrestrial ecosystems. Forests on dynamic floodplain landscapes, such as those created by river meandering processes, are characterized by uneven-aged trees and exhibit high spatial variability, reflecting the influence of interacting fluvial, hydrological, and ecological processes. Detailed and accurate mapping of aboveground biomass (AGB) on floodplain landscapes characterized by uneven-aged forests is critical for improving estimates of floodplain-forest carbon pools, which is useful for greenhouse gas (GHG) life cycle assessment. It would also help improve our process understanding of biomorphodynamics of river-floodplain systems, as well as planning and monitoring of conservation, restoration, and management of riverine ecosystems. Using stochastic gradient boosting (SGB), multivariate adaptive regression splines (MARS), and Cubist, we remotely estimate AGB of a bottomland hardwood forest on a meander bend of a dynamic lowland river. As predictors, we use 30-m and 10-m multispectral image bands (Landsat 7 ETM+ and SPOT 5, respectively) and ancillary data. Our findings show that SGB and MARS significantly outperform Cubist, which is used for U.S. national-scale forest biomass mapping. Across all data-experiments and algorithms, at 10-m spatial resolution, SGB yields the best estimates (RMSE=22.49tonnes/ha; coefficient of determination (R2)=0.96) when geomorphometric data are also included. On the other hand, at 30-m spatial resolution, MARS yields the best estimates (RMSE=29.2tonnes/ha; R2=0.94) when image-derived data are also included. By enabling more accurate AGB mapping of floodplains characterized by uneven-aged forests, SGB and MARS provide an avenue for improving operational estimates of AGB and carbon at local, regional/continental, and global scales.

Pain Without Gain: Land Assembly & Acquisition for Infrastructure Megaprojects the Indian Experience with the Bangalore International Airport

This presentation was made in the International Public Policy Conference in IIM Bangalore in August 2013. It traces the complex and meandering process of land acquisition and the micro managerial processes of decision making for the Bangalore international Airport. The qualitative case study analysis on infrastructure PPP mega projects throws up surprising findings that challenge popular perceptions about this slice of contemporary history; as well as theoretical perceptions in scholarship about the way governments work.